Real Space Imaging of Structurally and Compositionally Complex Materials

COFFEE_KLATCH · Invited

Abstract

High-Angle-Annular Dark-Field Scanning Transmission Electron Microscopy (HAADF/STEM) is a technique uniquely suited for detailed studies of the structure and composition of complex materials and allows us to speed up structural investigations in comparison to powder diffraction. The Mo-V-Nb-(Sb,Te)-O system has been identified as a commercially viable catalysts for the selective oxidation and ammoxidation of small alkanes to make about 25% of important organic chemicals and intermediates used in industry. The difficulty plaguing conventional crystallographic refinements of such a complex material is that the model has up to ~200 crystallographic parameters, requiring very high quality data and suitable starting models with imposed bond distance and angle constraints to reduce parameter space and ensure a stable and converging refinement. The availability of aberration-corrected electron microscopes has transforming imaging at the nanometer scale. Recent work also significan tly advanced the complexity of “frozen-phonon” calculations now possible to simulate HAADF-STEM images using massively parallel computations. In-situ heating in a STEM has revealed very unique thermal behavior and imaging at various temperatures helps us understand the operation of these catalysts near operando conditions .

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Authors

  • Brad Cox

    North Carolnia State University, Vanderbilt University, University of South Carolina, University of Virginia, Francis Marion Univ, Oak Ridge National Laboratory, Massachusetts Institute of Technology, Florida International University, Georgia College, JINR, Tsinghua University, LBNL, GANIL, Austin Peay State University, Lehigh University, University of Pardubice, Universit\'e de Rennes, Austin Peay State University Department of Physics and Astronomy, Oak Ridge National Laboratory, Oak Ridge TN 37831, American Superconductor Corp., Westborough MA 01581, University of North Georgia, Dahlonega GA 30597, Florida State University, Ecole Polytechnique, Space Telescope Science Institute, Fermi National Accelerator Lab, National Optical Astronomy Observatory, Austin Peay State Univerity, North Carolna State University, Florida Intl Univ, University of North Georgia, Clemson University, Clemson Univ, Vanderbilt University/ORNL, Vanderbilt University/Univ. of Kentucky, College of William and Mary, Louisiana State University, Presbyterian College, North Carolina State Univ, Department of Physics, Virginia Tech, Mathematical Institute, University of Oxford, Virginia Tech University, Hollins University, University of Tennessee Space Institute, Davidson College, University of Tennessee, American Superconductor Corporation, University of South Alabama, North Carolina State University, James Madison University, Lousiana State University, Korea Electrotechnology Research Institute, Changwon Korea